WO2010037485A1

WO2010037485A1 - Arrangements and method for measuring an eye movement, particularly a movement of the fundus of the eye

Info

Publication number: WO2010037485A1
Application number: PCT/EP2009/006816
Authority: WO
Inventors: Daniel Bublitz; Stefan Richter
Original assignee: Carl Zeiss Meditec Ag
Priority date: 2008-09-30
Filing date: 2009-09-22
Publication date: 2010-04-08
Also published as: JP2012503996A; US20110176110A1; JP5512682B2; US8596786B2

Abstract

In addition to a first detector for capturing a potential movement field of the eye in overview images, a second detector is used to capture a particular section of the eye in sectional images. From a displacement between two overview images and an intermediate displacement between two sectional images taken between said overview images, the eye movement is determined by linking said displacements. The sections are preferably illuminated by coherent light such that interfering light diffused on the eye produces a patch pattern. Alternatively, the sclera of the eye is illuminated with coherent light such that light diffused on the sclera produces a patch pattern, of which a particular part is captured using a spatially resolving detector in sectional images, on the basis of which an intermediate displacement is determined.

Description

Arrangements and methods for measuring an Auqenbewequnq. in particular a movement of Auoenhinterqrunds

The invention relates to arrangements and methods for (fast) measuring a movement of a human eye, in particular an ocular fundus, by means of a two-dimensionally spatially resolving detector for repeatedly recording a potential field of motion of the eye in overview images.

In ophthalmology and other fields of application, motion tracking devices have been used for some time to measure and track eye movement, among other things for research, diagnostic and therapeutic purposes, such as in the treatment of the eye (cornea, retina) It is important to ensure that the entry of light energy actually occurs at the pre-treatment sites in the eye to prevent damage to the eye, either by shutting off the laser as soon as eye movement is detected or by tracking Further fields of application of the eye movement measurement are controls of machines, for example computers or motor vehicles.

In the prior art, the pupil of the eye is usually recorded by means of a high-speed video camera at a high frame rate repeatedly in succession in images, for example according to WO 01/89438 A2. In the recorded images, the relatively sharp boundary between the black eye pupil and the brighter iris can be identified by means of special image evaluation algorithms, for example by edge detection. From shifts of this boundary or the center of the pupil in successive images, in principle, the eye movement can be determined. In order to capture low amplitude eye movements, the images must be taken with high optical resolution and sharpness. In order to be able to detect eye movements of large amplitude, the potential field of motion of the pupil must be included as much as possible in the pictures. The combination of both requirements requires the inclusion of images with a high number of pixels.

The reading out of such large images from the camera sensor and the subsequent evaluation of at least image parts, however, take a relatively long time due to the amount of data, so that only low effective refresh rates, ie the frequencies for the recording including the subsequent evaluation of a maximum of several 100 Hz can be achieved. However, the human eye can perform so-called saccade movements at speeds up to about 600 ° per second. In order to achieve a high accuracy of the motion measurement at such speeds a significantly higher effective refresh rate can be achieved. For example, tracking a therapy laser during a femtosecond Lasik operation would require an effective refresh rate of at least 1 kHz. This can be achieved in the prior art only by limiting the spatial resolution or the considered maximum motion field.

In the measurement of the movement of the fundus, in particular during a treatment of the retina, for example a laser photocoagulation, there is the additional problem that the necessary illumination may only take place in the infrared (IR) wavelength range in order to avoid glare and thus a blink reflex but the fundus in the IR area is low in contrast. For example, IR illumination is used on nonmydriatic fundus cameras during alignment and adjustment. Only for a color image is visible light irradiated for a short time, which typically leads to eyelid closure only after the end of the image exposure time. In order to determine a movement of the ocular fundus, in particular for tracking a laser, with sufficient accuracy, the recorded IR images must be evaluated in much larger image portions due to the low contrast than for an edge detection on the pupil. This further reduces the effective refresh rate. Alternatively, the movement of the fundus can be determined from a change in position of larger blood vessels. However, since the ocular fundus has few major blood vessels, only a small portion of the ocular fundus may be responsible for this type of evaluation can be used so that only in a limited field of motion can be measured.

In addition to motion measurement from video recordings, ocular fundus movements can be measured with scanning laser motion sequencing devices, such as those known from US 2006/228011, US 6,726,325, and US 5,644,642, which sample as highly structured a part as possible The scan can be done in a circle around a thicker branching of the trunk or around the optic disc of the eye.These systems have the advantage that the sensors can be adjusted to the geometry of the special eye, so that they only need a few points The disadvantage is that a complex laser scanning unit ("Laser Scanner") is needed.

The invention has for its object to improve an arrangement and a method of the type mentioned in such a way that with high spatial accuracy of measurement with little effort, a higher effective refresh rate is made possible as in the prior art.

The object is achieved by the feature combinations specified in the independent claims.

Advantageous embodiments of the invention are specified in the dependent claims.

According to the invention, it has been recognized that in the measurement of an eye movement, the effective image repetition frequency can be significantly increased by combining a large-format, slow movement measurement arrangement with a fast, small-format movement measurement arrangement.

According to the invention, it is therefore provided that in addition to the first two-dimensionally spatially resolving detector for repeated recording of a potential Motion field of the eye in overview images, each containing a first number of pixels, with a first frame rate in addition a second two-dimensional spatially resolving detector for repeatedly recording a respective section of the eye in excerpts, each containing a first number of pixels, with a second refresh rate, which is higher than the first refresh rate, and a computing unit for determining an intermediate shift based on two indirectly or immediately successive overview images and an intermediate shift on the basis of two indirectly or immediately successive, temporally recorded between these overview images section images and for determining a movement of the eye by concatenating this Shifts are arranged. A shift in the sense of the invention is, for example, a two-dimensional vector. For example, such a vector may describe an offset between the images. As concatenation is understood in the context of the invention, the series connection of the two shifts, for example by vectorial addition. When determining the movement, the determined two-dimensional displacement is expediently converted to a two-dimensional rotary movement. After determining the movement, this is expediently output for further processing.

Advantageously, the second number of picture elements is smaller, in particular significantly smaller, than the first number of picture elements in order to achieve the higher second picture repetition frequency. Due to the smaller number of pixels of the section images, their evaluation for determining the displacement can also be carried out more quickly.

The increase in the effective image repetition frequency for the measurement of eye movement is achieved by this combination of features, in that the measurement of the eye movement, in simple terms, is interpolated in the time between the overview images taken with a low frame rate by means of the image sections taken at a higher image repetition frequency. The shifts extracted from the high-resolution overview images comprising the entire potential motion field are used for recalibration in order to allow error propagation of the shifts extracted from the section images avoid. The recalibration succeeds preferably by comparing the last taken overview image with always the same (constant), preferably taken at the beginning of the process earliest overview image. Advantageously, a quasi-absolute starting position of the eye in this earliest overview image can be determined by manual or automatic (for example by means of image processing algorithms) comparison with a previous treatment planning acquisition. The shifts from the smaller section images can be detected at high speed, so that a high effective refresh rate is achieved. Due to this high effective refresh rate, a therapy laser can be tracked to planned light energy inputs with high spatial-temporal accuracy.

Preferably, the shifts are determined by comparing at least a respective part of the image content of the two images in question, for example by means of cross-correlation. In this way, two-dimensional displacements can be determined with little effort. The use of the correlation technique is described in US 5,786,804, the disclosure of which is incorporated herein in its entirety. For example, an optimized comparison may be made by primarily examining a direction of motion known from a previous displacement. Only if the test shows that the movement in this direction has not continued, are the other possible directions checked secondarily.

In a particularly preferred embodiment, a first light source for illuminating the potential field of motion of the eye with incoherent light and a second light source for illuminating the respective section of the eye with coherent light are provided such that in the respective section by interfering coherent light scattered on the eye The pattern is formed on the eye by the scattering of a microstructure in the volume of the eye tissue, for example in the dermis (Sclera) or the retina (retina). By generating and recording the high - contrast stain pattern in the Sectional images can be a displacement and thus the eye movement in a low-contrast area of the eye, for example, the dermis or, in the infrared region, the retina, determined as the stain pattern moves in an eye movement to the same extent. The shift of the speckle pattern can be determined, for example, by an image comparison by means of cross-correlation. The correlation of speckle patterns is described for example in JP 60174905.

In this case, the second detector preferably has optics for enlarged imaging of the spot pattern on the second detector in such a way that individual spots of the spot pattern have a size which corresponds to or is greater than a size of picture elements of the second detector. Thereby, the shift of the patch pattern between the patch images can be detected with high accuracy.

To measure a movement of a background of the eye, the first light source for illuminating the fundus of the eye is advantageously formed with infrared light, the first detector for recording at least part of the fundus formed as a potential field of motion of the eye and the second light source for illuminating a respective section of the fundus with infrared light educated. Through the use of infrared light, glare and thus a blink reflex are avoided when measuring the movement of the fundus.

Preferably, the second light source is designed for a flat illumination angle between 1 ° and 10 °. As a result, an excessively high energy density, as arises, for example, in the case of confocal point illumination, is avoided.

By substantially punctiform formation of the second light source in the plane of the eye pupil disturbing light reflections on the eye, especially on the front of the cornea (cornea), can be avoided or at least reduced. This can be realized, for example, by a substantially annular formation of a second light source plane conjugated to the eye pupil become.

Preferably, the second light source is configured to focus the coherent light in a plane conjugate to a pupil of the eye. Due to the conjugated arrangement, the arrangement according to the invention can be integrated with little effort in a conventional fundus camera.

Advantageously, the imaging and illumination beam paths are formed so that a mean direction of incidence of the coherent light of the second light source to the eye substantially coincides with an observation direction of the second detector. This can be achieved, for example, by coupling the imaging and illumination beam paths by means of one or more beam splitters / combiners. In particular, this succeeds with mirrors which reflect a geometric part of the respective beam path and leave untouched another geometric part, for example ring mirrors.

The arrangement according to the invention can be realized with little effort by using a detector of a laser mouse for the second detector. Such detectors are available inexpensively due to large numbers and standard electronics. An evaluation unit for the formation of correlations between successive cut-out forms is typically integrated in such detectors.

Preferably, the second detector is arranged in a plane which is optically conjugate to the respective cutout. The respective section lies in the case of measuring the movement of the fundus in the fundus, so that the second detector is conjugated to the fundus. Due to the conjugated arrangement, the arrangement according to the invention can be integrated with little effort in a conventional fundus camera.

The arrangement according to the invention can be used particularly advantageously in a fundus camera or in an ophthalmic laser system as a movement sequence arrangement for a therapy laser and / or for switching off the therapy laser upon detection of (for example, too great) eye movement be used. As a result, surgical procedures, laser photocoagulation or photodynamic therapies (PDT) in the fundus can be performed with high accuracy.

The fundus camera or the laser system preferably has a reflection-free front objective for illumination and detection or, in relation to the arrangement according to the invention, extra-axial illumination and detection. In this way, disturbing light reflections on the front lens can be avoided.

According to the invention, it has further been recognized that an eye movement with sufficient accuracy for some applications can also be determined exclusively by means of a single fast detector, by illuminating a dermis of the eye with coherent light during the repeated acquisition of detail images by means of the two-dimensionally spatially resolving detector, a staining pattern is produced by interfering light scattered on the dermis, wherein the detector must be designed to receive at least a part of the stain pattern in the excerpt images. A shift in the sense of the invention is, for example, a two-dimensional vector. For example, such a vector may describe an offset between the images. A movement of the eye can then be determined, for example by a computing unit, on the basis of an intermediate displacement of the speckle pattern, which is determined on the basis of two detail images. On a complex evaluation of the image content, for example by edge detection, can be dispensed with, since at a high refresh rate only a few pixels must be evaluated in order to determine the displacement of the speckle pattern can. Preferably, the arithmetic unit determines the shift by comparing the image content of the respective clipping images, for example by means of correlation. After determining the movement, this is expediently output for further processing.

Preferably, the detector has optics for magnifying the spot pattern onto the detector such that individual spots of the speckle pattern have a size about the size of pixels of the detector is equal to or greater than this. Thereby, the shift of the speckle pattern between the crop images can be detected with high accuracy.

Preferably, the coherent light source is designed for a flat surface illumination between 10 .mu.m.times.10 .mu.m and 1 mm.times.1 mm. As a result, an excessively high energy density, as arises, for example, in the case of confocal point illumination, is avoided.

Advantageously, the imaging and illumination beam paths are designed so that a mean direction of incidence of the coherent light on the eye substantially coincides with an observation direction of the detector. This can be achieved, for example, by coupling the imaging and illumination beam paths by means of one or more beam splitters / combiners.

The inventive arrangement can be realized with little effort by a detector of a laser mouse is used for the detector. Such detectors are available inexpensively due to large numbers and standard electronics. An evaluation unit for the formation of correlations between successive cut-out forms is typically integrated in such detectors.

The arrangement according to the invention can be used particularly advantageously in a fundus camera or in an ophthalmic laser system as a movement following arrangement for a therapy laser and / or for switching off the therapy laser upon detection of (for example, too great) eye movement. As a result, surgical procedures can be performed with high accuracy.

The fundus camera or the laser system preferably has a reflection-free front objective for illumination and detection or, in relation to the arrangement according to the invention, extra-axial illumination and detection. In this way, disturbing light reflections on the front lens can be avoided. Particularly preferred embodiments are those in which, for example by the arithmetic unit, more than two recorded clipping images are mosaically combined to form an overview image based on the respectively determined displacement, wherein the displacement of the speckle pattern for the respective last clipping image by comparing the image content of this clipping image with the image content of the overview picture. As a result, the error propagation during the shift during several follow-up shots can be reduced.

The invention also includes computer programs and control units for carrying out one of the methods according to the invention, in particular data carriers containing such computer programs, and ophthalmological devices comprising an arrangement according to the invention.

The invention will be explained in more detail by means of exemplary embodiments.

In the drawings show:

1 shows a conventional fundus camera,

FIG. 2 shows a high-quality infrared fundus image, FIG.

3 is a schematic representation of a fundus camera with fast and slow motion measurement arrangement,

4 shows a schematic representation of an illumination beam path,

Fig. 5 is a captured on a demonstration eye excerpt image with a speckle pattern and

Fig. 6 is a schematic representation of an eye movement follower arrangement with only one detector. In all drawings, like parts bear like reference numerals.

When illuminating a diffusing surface, such as paper or a wall, with a laser or other spatially and temporally coherent light source, the light backscattered from the surface may interfere with the space, leaving a typical pattern of granular structures or speckles. A distinction is made between subjective and objective patches, subjective patches arise when the scattering surface is imaged onto the camera sensor with an optical system, and the subjective patches are just as large as the optical resolution of the imaging system The pattern of speckles that is then registered moves with the scattering of the diffusing surface and thus enables a quantitative determination of the displacement. "Objective stains arise when the camera sensor without optics is placed in the light backscattered by the specimen." Objective stains respond to tilting of the specimen The size of the objective spots is calculated from the wavelength of the radiation, the diameter of the illuminated sample surface and the distance between the sample surface and the camera sensor. The following quantities can be measured, in particular in one eye, inter alia with the spot correlation technique:

a) Measurement of the distance of a scattering surface of a contact surface, for example, for autofocusing. A laser wave with a specific aperture is focused on the sample surface. The backscattered from the surface of the sample light wave is registered with a camera sensor without optics. The average size of the objective spots is determined by determining the half width of the autocorrelation function of the camera images. This half width is directly proportional to the diameter of the illuminated surface at fixed wavelength and distance of the camera from the scattering surface. Since the focusing of the illumination wave, the diameter of the illuminated surface depends on the distance of the scattering surface of the focal plane of the illumination wave, a distance sensor can be realized in this way.

b) Measurement of the displacement of a scattering surface: A laser wave is imaged on the sample surface to be measured. The backscattered from the sample Light is imaged on a camera sensor using an optical system. Due to the optical aberration, a certain part of the specimen is always imaged onto one point of the camera surface due to the aberrations and the diffraction diffraction. The object distribution is folded with the point-spread function (PSF) of the optical system, resulting in the image taken in. The coherence of the laser wave makes it possible to interfere with and produce the light incident on a pixel of the camera sensor This pattern of patches moves with the scattering surface during lateral displacements By forming the cross-correlation between two consecutively recorded images of the patches pattern, the size and direction of the patches can be determined The method is robust because it does not measure the structures of the sample, but rather the correlations in the backscattered light field, and the structuring of the image comes about through the coherent properties of the illumination wave in conjunction with the statistical phase variance the scattering on the surface. For cross-correlation small, low-resolution camera sensors with a few hundred pixels can be used, which enables very high measuring speeds in the kilohertz range. By combining the measurement of the objective and the subjective spots, a three-dimensional displacement vector can be determined. With several sensors, the changes in position and angle of a general area can be determined and thus the movements of a human eye in all degrees of freedom can be detected. A similar method for two-dimensional displacement determination is used in computer optical mice in which the correlations in backscattered light from the table are measured.

In order to realize a motion measurement optimized for speed and accuracy, first the motion degrees of freedom of the system have to be determined. These degrees of freedom of movement can very much depend on the application to be implemented. In principle, the eye can move along with the head in all three spatial directions or tilt by three angles. In addition, the eye can rotate in the eye socket by two angles (horizontal, vertical). So to measure all the movements of the eye, so would the determination of three Shifts and three angle changes needed. However, for some ophthalmic applications, the movement of the eyes is measured and compensated for only about 1 second. In this case, not the head movements, but only the fast eye movements must be measured. In this case, two degrees of freedom (horizontal and vertical rotation angle), which can be measured with a sensor, are sufficient. In addition, in the case of refractive therapy of the cornea, an autofocus sensor would be required to measure the removal of the cornea from the treatment device.

First, the measurement of the movement of the fundus in a fundus camera will be considered. For this purpose, FIG. 1 shows a conventional fundus camera 1. In the illumination beam path B, it has a light source 3 with optical elements 4 for focused illumination of the background 6 of the eye 2. The imaging beam path A is reflected by a beam splitter 7 in the illumination beam path B and contains a detection optics 9 for imaging the ocular fundus 6 on the spatially resolving detector 10. The fundus camera 1 is operated by a control unit 14, on the one hand with the detector 13 and on the other hand with the light source 3 is connected.

Fig. 2 shows an infrared fundus recording high quality. Nevertheless, the contrast is low, so that a shift between two successive shots, for example by correlation, only with great effort (correlation of large image areas) and therefore can be determined slowly.

FIG. 3 schematically illustrates a fundus camera 1 according to the invention with a fast and a slow movement measurement arrangement. The slow motion measurement arrangement comprises a first incoherent IR light source 3 and a first IR detector 10 including detection optics 9A. The fast motion measurement arrangement comprises a second, coherent IR light source 12 for generating a speckle pattern by interference and a second IR detector 15 including detection optics 9B for receiving the speckle pattern. Both detectors 10, 15 are connected to a computing unit (not shown), the continuous means of the first detector 10 overview images of the entire potential field of motion of the fundus 6 and by means of the second detector 15 accepts sectional images of the fundus 6.

The slow movement measurement arrangement has the advantage that it allows very reliably the displacement of the fundus in quasi-absolute coordinates and thus the reference to a previous Fundusaufnahme. This makes a pre-planning of treatment / diagnostics possible. In addition, relatively strong fundus deflections can be detected with the aid of the slow movement measurement arrangement with its relatively large image field. The fast motion measurement arrangement has the advantages of a very short latency, a high speed and a high reliability of the motion measurement even when measuring in blurred and poorly structured fundus areas. It has the disadvantage that it can only be measured relative shifts, so that on this basis alone no treatment planning is possible. In addition, computational errors add up by the pairwise comparison of consecutive images and thus can lead to larger errors in the coordinate computation of the total displacement due to error propagation.

For this reason, first, the displacement of the fundus with respect to an earlier photograph is performed to schedule the slow motion measurement treatment. Thereafter, with the fast movement measurement arrangement, the movement of the fundus is continuously detected. For example, twice a second, an overview image is captured and evaluated using the slow motion measurement arrangement, comparing it with the earlier planning shot. The movement determined therefrom serves to recalibrate the coordinate system of the fast motion measurement arrangement by concatenating the determined displacements.

Operating principle of the slow movement measurement arrangement: The entire fundus 6 is illuminated with a first IR light source 3, for example an IR LED or a white light lamp with a spectral filter. The light backscattered by the eye behind approximately 6 is imaged onto a spatially resolving detector 10, for example a CMOS or CCD camera. There are overview images with a refresh rate between 1 Hz and 30 Hz (frames per second) and displayed on a computer monitor (Fig. 2). The hardware for this slow part of the combined motion measurement arrangement is already engineered in all nonmydriatic fundus cameras as an IR monitor or IR adjuster. From the overview fundus images recorded in this way, a square image field with 2 ⁿ × 2 ⁿ pixels is cut out, which contains as many specific structured image details as possible. All overview images are cross-correlated against the first overview image, thus determining the displacement of each of the overview images in relation to the first overview image. The first overview image may be the first image of a series of overview images, then the displacement of each further overview image relative to the first overview image is known. In a particularly preferred embodiment variant, a color image and an associated IR image of the fundus 6 are recorded with a standard fundus camera. With the aid of these images, the physician can plan the therapy / diagnosis to be performed, for example laser coagulation of areas of the ocular fundus 6. At the beginning of the therapy / diagnosis, a first IR overview image of the ocular fundus is recorded and correlated against the IR image of the therapy planning admission To determine the initial position of the fundus 6. The following overview images are then always correlated against the first overview image or against the IR image of the therapy planning admission. In this way, for example, previously planned points of the fundus can be approached and treated with a laser coagulator, since the movement of the fundus 6 in relation to the treatment planning is measured. The image field for the correlation is selected to be so large that the maximum amplitude of eye movements that occur in the specific case of observation (for example, supported by an internal fixation), ie the potential field of motion of the fundus 6, are smaller than the size of the image field. A certain minimum size, which depends on the optical quality of the overview images, must not be undercut so that the eye fundus movement can be reliably detected (this results in a preferred n = 6 ... 9).

The great advantage of the illustrated method is that it is already technically provided in any non-mediary fundus camera, and thus can be realized very inexpensively. However, since the process involves the use of standard Monochrome cameras, such as those used in a nonmydriatic fundus camera, are expected to have a typical readout time of at least 50 ms. The calculation of the cross-correlations should preferably take place in a standard computer contained in the fundus camera and thus requires, depending on the size of the image field to be correlated, approximately 500 ms. Thus, the 550 ms process is much slower compared to other state of the art motion measurement or motion tracking devices. For this reason, the slow motion measurement arrangement is combined with a second, independent system that enables fast motion measurement.

Working principle of the fast movement measurement arrangement: For the fast movement measurement arrangement, a small part of the fundus 6 is illuminated with a coherent IR laser illumination 12. The diameter of the coherently illuminated area in the fundus 6 is approximately between 1 ° and 10 ° at a flat angle, whereby the radiation exposure of the fundus 6 is as low as possible, and is thus significantly smaller than the field of view of the fundus camera detector 10. The illuminated area is however with between 1 ° and 10 ° significantly larger than that of a typical confocal point illumination. The light reflected from the ocular fundus 6 interferes in the form of a speckle pattern, which is recorded in section images with a spatially resolving detector 15 of low resolution. Examples of the technical design of the detector are CCD, CMOS or InGaAs cameras, wherein preferably only a small image section ("region of interest", ROI) is read out the spots caused by the coherent properties of the illumination source 12 are at least as large as the pixels of the detector 15.

From the detail images recorded in this way, the relative shift to the respective predecessor image or to a first excerpt image after recording a further overview image is then calculated via a cross-correlation or, alternatively, estimated via a consideration of the optical flow. Another way to increase the speed of calculating the cross-correlation is not to get all the points of cross-correlation to calculate. Only nine pixels (3x3) of the cross-correlation are calculated, namely the pixels of the expected shift between the two clipping images and its nearest neighbor in each direction. This is used to calculate the exact displacement (preferably with subpixel interpolation) and is used to estimate the shift to the next detail image. In the following excerpt image only the 9 pixels of the cross-correlation are calculated, which correspond to the expected shift between the two excerpts. This type of evaluation can reduce the computation time by a factor of 100 for a typical pixel array (for example, 30x30 pixels). The only requirement that has to be fulfilled is that the acceleration of the displacement must not exceed a certain limit.

The size of the recorded clipping images or the sub-images of the clipping images used for the correlation is approximately 10 × 10 pixels to 100 × 100 pixels, so that only relatively few data have to be evaluated and the evaluation thus becomes significantly faster. As a target specification, the fast movement measurement arrangement should preferably take a picture within 5 ms, read it and evaluate the displacement data. The evaluation can be carried out in a standard computer or preferably in a special evaluation, for example in a so-called smart pixel camera.

Due to the coherent illumination 6 structurally strong interference patterns are impressed on the relatively structureless Fundus, which can be registered much better. A further advantage of the method is that due to the specific properties of "speckle" spots a measurement of the movement of the fundus 6 is possible even in the not optimally focused state of the detector 15 (the detection optics 9B).

Particularly preferably, the recording and evaluation of the sectional images of the fast motion measurement arrangement with a commercially available laser mouse sensor. These sensors were designed to measure movements above a diffusing surface using specular reflections below the glancing angle, disclosed for example in US Pat. Nos. 7,161,682 B2 and US Pat US 5,786,804. However, the principle of evaluation, which is generally wired in the sensor, can surprisingly be used cost-effectively for the recording and evaluation of the patch pattern detail images. However, no specular reflections are evaluated in the embodiment variant shown here, since they essentially result from a 3D surface curvature of a scattering surface, while a approximately 0.5 mm thick volume scattering layer (retina) is to be detected on the ocular fundus 6. The same applies to alternative embodiments for measurement on the dermis.

The detector 15 of the laser mouse sensor is arranged in the fundus camera 1 in a plane ZB (intermediate image plane) conjugated to the fundus. In this case, either all the optics and beam-limiting surfaces located in the detection beam path in US Pat. No. 7,161,682 B2 are eliminated, or the image conjugated to the ocular fundus is arranged in the optimum focal point of the detection optics described therein. In both cases, the aperture of the optical detection system 9B is limited such that the resulting detection spots are larger than the pixels of the detector 15 by a diaphragm, or by selecting a corresponding magnification.

A fundus camera 1 essentially corresponds to a biological microscope with the aid of which the fundus of the eye can be depicted. Due to the specific geometry of the human eye, special technical design possibilities are provided in a fundus camera 1 in order to be able to record the best possible image of the fundus 6. One element of this specific optics is a ring illumination in the pupil 5 of the eye 2. This illumination is chosen to suppress a light reflection of the coma front in the detection beam path. For this purpose, a lighting ring 3 with, for example, 5.5 mm outside diameter and 3.5 mm inner diameter in the cornea plane of the human eye 2 is irradiated as a virtual illumination source, which illuminates the fundus 6 as evenly as possible to field angles of about 22 °. The radiation that is emitted, for example, by an annular fiber bundle 3 is imaged by optics 16 on an annular mirror 13, which is also in a conjugate to the eye pupil 5 level. The backscattered from the fundus 6 radiation transmitted through the hole in Ring mirror 13 and is imaged on the second detector 15. This second detector 15 is in an intermediate image plane ZB conjugated to the fundus 6. The structure thus described corresponds to a standard fundus camera and, in this embodiment, represents the slow part of the combined motion measurement arrangement.

For the fast part, coherent IR laser illumination 12 is collimated with optics 19A and then focused by a second lens 19B onto an annular aperture 14 located in a plane conjugate to the pupil plane, as shown in detail in FIG. The coherent IR light is then superimposed on the illumination beam path of the first incoherent IR light source 3 via a dichroic or semitransparent mirror as beam combiner 20 (FIG. 3). The IR light is then directed through the optics 16, 4 of the fundus camera 1 to the fundus 6 and illuminates there a surface with a flat diameter between 1 ° and 10 ° (Fig. 3).

The backscattered light from the fundus 6 is split off from the fundus beam path by another dichroic or partially transmissive mirror 7 and imaged onto the second detector 15 conjugated to the fundus 6 (FIG. 3). By illuminating the fundus 6 with coherent light and imaging the backscattered light onto the second detector 15, two types of spots are created, subjective spots and objective spots. The subjective detection spots are utilized to measure the movement of the fundus 6, while the objective illumination spots are a disturbance. In order to limit the interfering influence of the objective illumination spots, the coherent illumination is preferably focused in a plane conjugated to the eye pupil (annular stop 14). As a result, the illumination spots in the fundus 6 have a size which corresponds approximately to the beam diameter in the fundus 6 and therefore no longer pose a problem for the further method. Semiconductor laser sources are preferably used for the second light source 12, but all other types of coherent light sources are also used Coherence lengths greater than about 0.5 mm (the coherence length should preferably be at least twice the thickness of the retina to allow good pattern patching on the detector 15) reach) and good spatial coherence for the method can be applied.

Another specific feature of fundus camera illumination optics is the introduction of antireflection points (apertures) in the illumination beam path, which are intended to prevent reflections on the front objective of the fundus camera into the detection beam path. If these antireflection points are not optimally adjusted or if some of the optical elements of the illumination beam path are slightly scattering due to dust particles, the detector image of the fundus camera shows a typical annular reflex which also occurs in the laser emission path and can lead to problems in the motion measurement. For this reason, the use of a reflex-free front lens is particularly preferred. A second preferred variant when using standard lenses in the fundus camera is a slightly extra-axial illumination and an adapted extra-axial detection.

FIG. 5 shows a speckle pattern recorded with coherent illumination of an ocular fundus 6.

In refractive surgical treatment of the cornea, a contact lens is used to define the position of the eye in cases where a particularly high degree of accuracy is required (for example femtosecond-Lasik; fs- Lasik). In this case, a movement of the eye is theoretically not possible. However, with stronger forces between the eye and the contact lens, shifts of the eye can occur parallel to the contact lens. In this case, these shifts would need to be measured very quickly to track or turn off the therapy laser. Exactly this measuring task solves the arrangement according to the invention with only one detector particularly simple and cheap.

The basic structure of the movement measuring arrangement is shown in FIG. 6 in a schematic representation. The beam path of the Lasik laser (not shown) for the treatment of the cornea 16 remains unchanged. For the realization of the movement measurement arrangement, a highly coherent laser beam of the light source 12 is focused on the dermis 17 of the eye 2 in addition to the contact glass 18 or at the edge thereof through the contact glass 18. The sclera 17 Backscattered light is magnified by a detection optics (not shown) magnified on a single, spatially resolving camera sensor 15. Since only a very small image field has to be imaged onto the camera sensor 15, the requirements for the quality of the optics are relatively low. The resolution of the optical system is chosen to match the measurement accuracy of the motion measurement arrangement to be achieved. In the case of the fs- Lasik, the resolution should be between 1 μm and 3 μm. This requires a lens with a relatively high numerical aperture. A field of view with a diameter of about ten "speckle" spots is sufficient for the evaluation of the data, which corresponds to a field of view of about 10 μm at a resolution of 1 .mu.m Such small image fields can be used with illumination with strictly monochromatic laser light with relatively little effort During the movement measurement, the camera sensor 15 records section images of the dermis 17 with a very high refresh rate and calculates the cross-correlation of immediately successive images be dimensioned in its image field so that the shift between two section images is never larger than the image field of the camera sensor 15. It should be noted in this arrangement that only the relative displacement between the images can be calculated e absolute orientation of the eye with the number of clipping images is uncertain as the measurement errors propagate.

In order to be able to measure quasi-absolute movements or positions of the eye, the third detail image which is measured is not cross-correlated against the second detail image, but again against the first, and thus determines the shift to the first detail image. This succeeds as long as the relative displacements of the two images are smaller than the image field of the sensor. In order to develop a global scale, the different clipping images are combined in a mosaic-like manner to a full-surface overview image with the help of the correlation algorithms. An additional image is then correlated exclusively with a part of this global overview image. As a result of this evaluation method, the position inaccuracy no longer increases with the number of images, but only with the relative distance to the center of the image first excerpt image. With the displacement sensor thus described, a measurement accuracy between 1 .mu.m and 3 .mu.m can be achieved at an effective refresh rate of between 1 kHz and 10 kHz.

LIST OF REFERENCE NUMBERS

1 fundus camera

2 eye

3 First light source

4 front lens

5 pupil

6 background

7 beam splitter

8 aperture

9 detection optics

10 First detector

11 control unit

12 Second light source

13 ring mirrors

14 ring aperture

15 second detector

16 Cornea

17 dermis

18 cover glass

19 Illumination optics

20 beam combiner

A imaging beam path

B illumination beam path

Eg intermediate image plane f. f focal lengths

Claims

claims

1. Arrangement for measuring a movement of an eye (2), comprising a first two-dimensionally spatially resolving detector (10) for repeatedly recording a potential movement field of the eye (2) in overview images with a first image repetition frequency, characterized by a second two-dimensionally spatially resolving detector (15) for repeatedly recording a respective section of the eye (2) in sectional images having a second image repetition frequency which is higher than the first image repetition frequency, and an arithmetic unit (11) for determining an intermediate displacement based on two overview images and an intermediate displacement based on two excerpt images and for determining a movement of the eye (2) by concatenating these shifts.

2. Arrangement according to claim 1, characterized by

a first light source (3) for illuminating the potential field of motion of the eye (2) with incoherent light,

- A second light source (12) for illuminating the respective section of the eye (2) with coherent light such that in the respective section by interfering, the eye (2) scattered coherent light creates a spot pattern, and

- Formation of the second detector (15) for receiving at least a portion of the speckle pattern in the relevant section image.

Arrangement according to claim 2, characterized in that the second detector (15) has optics (9B) for enlarged imaging of the spot pattern on the second detector (15) such that individual spots of the speckle pattern have a size of approximately one size of pixels of the second detector (15) is equal to or greater than this.

4. Arrangement according to claim 2 or 3 for measuring a movement of a background of the eye (2), characterized by

- Forming the first light source (3) for illuminating the Ocular fundus (6) with infrared light,

- Forming the first detector (10) for receiving at least a portion of the ocular fundus (6) as a potential field of motion of the eye (2) and

- Forming the second light source (12) for illuminating a respective section of the ocular fundus (6) with infrared light.

5. Arrangement according to one of claims 2 to 4, characterized by forming the second light source (12) for a (planar) illumination angle between 1 ° and 10 °.

6. Arrangement according to one of claims 2 to 5, characterized by substantially punctiform formation of the second light source (12) in the plane of the eye pupil (5).

7. Arrangement according to one of claims 2 to 6, characterized by forming the second light source (12) for focusing the coherent light in a plane which is conjugate to a pupil (5) of the eye (2).

8. Arrangement according to one of claims 2 to 7, characterized in that a mean direction of incidence of the coherent light of the second light source (12) on the eye (2) substantially coincides with an observation direction of the second detector (15).

9. Arrangement according to one of the preceding claims 2 to 9, characterized by the formation of the second detector (15) as a detector of a laser mouse.

10. Arrangement according to one of the preceding claims, characterized by arranging the second detector (15) in a plane (ZB) which is optically conjugate to the respective section.

11.Anordnung according to any one of the preceding claims, characterized in that the arithmetic unit (11) the shifts by comparing at least a respective part of the image content of the relevant two images, with coherent illumination in particular by comparing at least a respective part of the recorded patch pattern, determined.

12. A method for measuring a movement of an eye, wherein by means of a first two-dimensionally spatially resolving detector repeatedly at least one potential motion field of the eye is recorded with a first refresh rate in overview images, characterized in that by means of a second two-dimensional spatially resolving detector repeatedly a respective section of the eye a second frame rate, which is higher than the first frame rate, is recorded in clipping images, wherein an intermediate shift is determined using two overview images and an intermediate shift using two clipping images and by moving the two shifts a movement of the eye is determined (and output).

13. An arrangement for measuring a movement of an eye (2), comprising a two-dimensionally spatially resolving detector (15) for repeatedly recording sections of the eye (2) in sectional images, characterized by

a light source (12) for illuminating a dermis (17) of the eye (2) with coherent light such that a staining pattern is produced by interfering light scattered on the dermis (17),

- Formation of the detector (15) for receiving at least a portion of the speckle pattern in the sectional images and

- An arithmetic unit for determining an intermediate displacement of the speckle pattern using two excerpt images and for determining a movement of the eye (2) based on this shift.

14. Arrangement according to claim 13, characterized in that the arithmetic unit determines the displacement by comparing the image content of the respective clipping images.

15. Arrangement according to claim 13 or 14, characterized in that the detector (15) has an optics for enlarged imaging of the speckle pattern on the detector (15) such that individual spots of the speckle pattern a Have size that corresponds to about a size of pixels of the detector (15) or greater than this.

16. Arrangement according to claim 13, 14 or 15, characterized by the formation of the light source (12) for a (planar) illumination surface between 10 microns ² and

1 mm ² .

17. Arrangement according to one of claims 13 to 16, characterized in that a mean direction of incidence of the coherent light of the light source (12) to the eye substantially coincides with an observation direction of the detector (15).

18. Arrangement according to one of claims 13 to 17, characterized by the design of the detector (15) as a detector of a laser mouse.

19. Arrangement according to one of the preceding claims 13 to 18, characterized by arranging the detector (15) in a plane which is optically conjugate to the respective cutout.

20. Arrangement according to one of the preceding claims, characterized by arrangement in a fundus camera (1) or in an ophthalmic laser system.

21.Anordnung according to claim 20, characterized by a reflection-free

Front lens for illumination and detection or by off-axis training of lighting and detection.

22. A method for measuring a movement of an eye, wherein repeated sections of the eye are taken in section images by means of a two-dimensionally spatially resolving detector, characterized in that a dermis of the eye is illuminated by means of a light source with coherent light such that by interfering, on the dermis scattered light a stain pattern is formed, of which by means of the detector, a respective part is included in the clipping images and that an intermediate Scouting zuminαesi of a part of the recorded patch pattern is determined based on two clipping images and based on this shift, a movement of the eye is determined (and output).

23. The method according to claim 22, characterized in that the shift is determined by comparing the image content of the respective two clipping images.

24. Method according to claim 22, characterized in that more than two recorded detail images are combined in a mosaic-like manner into an overview image on the basis of the respectively determined displacement, and that the displacement of the speckle pattern for the respectively last recorded detail image is compared to the image content by comparing the image content of this detail image of the overview screen.

25. Computer program, in particular data carrier with such a computer program, or control unit, set up for carrying out a method according to one of the method claims.